This invention relates to a motor driven power steering apparatus.
Japanese Kokai Publication No. 61-9370, published on January 16, 1986, discloses a conventional motor driven power steering apparatus. This apparatus comprises an input shaft connected with a steering wheel, an output shaft connected with road wheels, a torque detector for detecting an applied steering torque between the input and the output shafts, an electric motor for generating an auxiliary torque, an electromagnet clutch for selectively connecting the electric motor with the output shaft, and, an electric power controller for controlling magnitude and direction of the auxiliary torque based on the steering torque detected by the torque detector. The electromagnet clutch connects the electric motor with the output shaft whenever the torque detector detects a steering torque. At the same time, the electric motor generates proper auxiliary torque based on the detected steering torque. As a result, the output shaft is rotated with larger torque than the input shaft. Thus, a driver can handle the steering wheel lightly and easily.
The electric motor may be locked mechanically when a magnet is disconnected from a motor housing, when a brush unit is disconnected from the motor housing, or some other accident. If the electric motor is locked, the steering wheel may be locked, hence the electromagnet clutch connects to the locked motor with the output shaft when the steering wheel is rotated.